The present invention relates to a general service incandescent lamp, and more particularly, to a general service incandescent lamp having a substantially elliptical inner envelope with an outer surface coated with an infrared reflective film.
The continuing pursuit of improving the efficiency of lamps is of increasing importance due to the increasing cost of energy. One of the family of lamps in which the efficiency is desired to be improved is the incandescent lamp. Incandescent lamps, although having efficiency ratings lower than those of fluorescent and high intensity discharge lamps, have many attractive features, such as, low cost, compact size, instant light, dimmability, convenience, pleasing spectral distribution and millions of existing sockets in the homes of the users who have become accustomed to incandescent lighting.
Incandescent lamps come in various sizes, the most well-known being that of the A-line which is typically termed a general service incandescent lamp and is available in a wide range of wattage ratings. Still further, the general service incandescent lamp typically has a tungsten filament.
The tungsten filament is also commonly utilized in relatively more expensive but more efficient special purpose halogen type lamps. In typical operation of the general service incandescent lamp over an extended period of time, some tungsten of the filament evaporates and becomes deposited on the wall of the outer envelope, which, typically causes a darkening of the envelope, which, decreases the lumen output thereby decreasing the lumens per watt or efficacy of the lamp. It is known that the darkening of the envelope caused by the evaporation of tungsten filament material can be substantially reduced by providing a halogen doped gas atmosphere surrounding the tungsten filament effective to provide a regenerative (transport) cycle that keeps the walls of the envelope clean and thereby the noted decrease in lumen output is eliminated or reduced.
The use of a halogen doped gas adapted to the relatively inexpensive general service incandescent lamp is described in the aforementioned U.S. application Ser. No. 519,165. The halogen atmosphere of the aforementioned U.S. application Ser. No. 519,165 is considered desirable for the present invention along with additional improvements of this invention related to the general service incandescent lamp.
The performance of a tungsten filament of the incandescent lamp can be further improved by housing the filament in a suitable fill-gas, such as xenon, krypton or argon, raised to a pressure significantly above atmospheric. The high pressure fill-gas improves the performance of the lamp by reducing the evaporation rate of the tungsten from the filament, thereby increasing the life of the filament when operated at the same temperature. Alternatively, the reduced evaporation rate of tungsten from the filament permits one to raise the filament operating temperature while maintaining the same life. Operating the filament at higher temperatures increases lumens and efficacy.
The arc-out resistance of the filament, that is, the resistance of the filament to being burned out by an arcing condition within its housing, may be improved by the addition of nitrogen. The aforementioned U.S. patent application Ser. No. 519,165 discloses an incandescent lamp utilizing the efficacy gain realized by the high pressure fill gas of the xenon, krypton or argon, and to improve the arc-out resistance of the filament by the addition of the nitrogen gas. It is considered desirable to operate the tungsten filament within the relatively high pressure fill-gas having nitrogen additive along with further improvements of the present invention.
Another means for extending the life of an incandescent lamp is to reduce the operating voltage of the filament, but it is desired that this reduction of operating voltage be accomplished while maintaining the wattage and efficacy of the lamp. The U.S. patent application Ser. No. 519,165 discloses a specially suited filament that provides extended life and maintains the wattage of the lamp. Alternatively, the efficacy of a low voltage incandescent filament can be increased while maintaining life. Further still, a low voltage filament, such as described in U.S. patent application Ser. No. 519,165, is advantageous in that the low voltage filament is mechanically sturdy with a stable configuration. It is considered desirable to provide a specially suited filament along with further improvement of this invention for a general service incandescent lamp.
Still further, means for improving the operation of the incandescent lamp may be accomplished by the utilization of an infrared film such as described in U.S. Pat. No. 4,017,758, United Kingdom (UK) Patent Specification No. 884,087, or the aforementioned U.S. application Ser. No. 519,162. It is considered desirable to provide an infrared film for an incandescent lamp arranged in accordance with the practice of this invention so that substantially all of the filament radiation is returned or reflected back to the filament by a shaped inner envelope which is a substantially ellipsoid configuration the foci of which are at the ends of the lighted portion of the filament. Further, the practice of this invention is such that the returned radiation is distributed in a nearly uniform manner along the filament. Additionally, the practice of this invention provides a shaped inner bulb having an infrared reflective coating that results in a highly improved efficacy for a general service incandescent lamp.
Still further, with regard to improving a general service incandescent lamp the shape of the surface on which the infrared film is placed should be considered with regard to the interrelationships of the dimensions and placement of the filament relative to the infrared film. For example, during the manufacturing process the location of the filament within the incandescent lamp may inadvertently vary slightly relative to the desired location of the infrared film. This slight variation may hinder the redirection of the infrared radiation by the infrared film back toward the filament so that the reflected radiation may completely miss or not intercept and impinge upon the filament. The effect of the variation between the desired and actual location of the filament relative to the infrared film increases as the distance between the filament and infrared film increases. It is therefore considered desirable to provide a shape that has on its surface an infrared film which is relatively close to the location of the filament.
Further still, if an infrared film placed on a desired surface is used in an incandescent lamp in conjunction with a halogen doped gas atmosphere, the shape of the desired surface should take into consideration the operation of that gas atmosphere. For example, the performance of a halogen doped gas atmosphere in providing its cleaning action related to a tungsten film deposited on the glass wall is dependent upon the temperature of the wall. A substantially uniform temperature distribution on the inside wall of the shaped envelope which contains the halogen doped gas is beneficial to the performance of the halogen gas. It is considered desirable to provide a predetermined shaped surface for placement of the infrared film so that the shape contributes to providing an envelope containing the halogen doped gas having a substantially uniform temperature distribution on its inside surface.
Although all of the above considerations are of primary importance to the present invention, a still further consideration is the practical consideration of providing a desired infrared film in an inexpensive manner. For example, if the IR film is placed on a relatively small device the cost of the IR film can be reduced so as to contribute to providing a relatively inexpensive incandescent lamp while still improving its efficacy.
Accordingly, objects of the present invention are to provide a relatively inexpensive general service incandescent lamp having, (1) a fill gas such as xenon, krypton, or argon all of a pressure significantly above atmospheric, both the fill-gas and the high pressure contributing to improving the operation of the filament, (2) a relatively high pressure fill-gas having an addition of nitrogen so as to improve the arc-out resistance of the filament, (3) a relatively high pressure fill-gas having an addition of halogen gas so as to provide a transport cycle for the evaporated tungsten, (4) a specially adapted filament operated at a low voltage so as to extend the life of the incandescent lamp while still maintaining the wattage of the lamp and even increasing the efficacy of the lamp, (5) a low voltage filament which is mechanically sturdy and has a stable configuration, (6) an infrared film placed onto a desired shape in which, (a) the infrared radiation reflected by the infrared film is returned to the filament so as to substantially enhance the efficacy of the lamp, (b) the placement of the infrared film on the desired surface reduces the effect of variations between the desired and actual locations of the filament relative to the infrared film, (c) the desired shape having the infrared film provides a substantially uniform temperature distribution for housing the halogen gas so as to enhance the operation of the halogen gas atmosphere, and (d) the infrared film is provided for the incandescent lamp in a relatively inexpensive manner, and (7) combining all the six objective features of this invention in such a manner that the overall effects thereof extend the life of the incandescent lamp and provide an improved efficacy both greater than the expected gains usually realized from the individual six features of this invention.
These and other objects of the invention will become apparent upon consideration of the following description taken together with the accompanying drawing.